Slow VM with enabled GPU passthrough (kvm=off or hidden=1)


Dec 30, 2019

I am running Proxmox 6.1 and I am passing an RTX 2070 to my VM (Ubuntu 18.04). In order to avoid Error 43, I had to set hidden=1 or pass the argument kvm=off. However, with this configuration I am loosing between 20-50% single core performance.

Interestingly, glances is reporting that the CPU is spending about 80% of its time running code in the Operating System kernel. As soon as I remove kvm=off, the CPU spends 95% of its time on my test program.

What is the reason for this and is there any workaround?

This is my VMs configuration file:
agent: 1,fstrim_cloned_disks=1
args: -cpu 'host,hv_vendor_id=NV43FIX,kvm=off'
balloon: 0
bios: ovmf
boot: dcn
bootdisk: scsi0
cores: 30
cpu: host,flags=+aes
efidisk0: local-lvm:vm-101-disk-0,size=4M
hostpci0: 08:00,pcie=1
hotplug: 0
ide2: none,media=cdrom
kvm: 1
machine: q35
memory: 29000
name: gpu-node1
net0: virtio=B6:7A:11:51:8F:31,bridge=vmbr0
numa: 0
ostype: l26
parent: TF
scsi0: local-lvm:vm-101-disk-1,size=50G,ssd=1
scsihw: virtio-scsi-pci
smbios1: uuid=737bd9ee-5db8-4b2d-bc3f-e2f4fd336e80
sockets: 1
vmgenid: 9ccac038-a498-40aa-9194-5c45728feaf4
Last edited:
After further testing, the issues seems to only ocurre if I assign more than 1 vCPU to the VM. WIth only 1 vCPU everything works fine.
Last edited:
Further testing shows that the problem also occures on Proxmox 5.4. It also seems to be no hardware issue, since the system performs perfectly with ESXI.

It would be great, if there exist a solution, since I just moved from ESXI to Proxmox and I really like it.

I add my exact harware specifications:
> Ryzen 3950x
> ASUS x570 TUF Gaming (Wifi)
> MSI RTX2070 Aero
hi. i also notice this (kinda)

i have a Windows VM that i use for gaming, and lately i started feeling Audio and I/O glitching.

Not sure if its CPU related tho.

Have you managed to fix your problem?



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